Evolution of the surface layer appearing with the corona ageing of epoxy samples

The impact of ions, photons and neutral activated particles produced by a corona can be an important parameter in the mechanism of polymeric indoor HV insulation ageing. Corona treatment is known to induce a wettability increase on polymer surfaces, and can thus be one of the first steps towards the emergence of a wet conductive layer on the surface. Therefore, this chemical influence of the discharge on the surface greatly influences the flashover voltage. We present here optical and electrical measurements on epoxy samples submitted to the activated species produced by an alternating corona discharge. Corona treatment on polymers by the means of an AC corona discharge is of common industrial use nowadays to increase the wettability and adhesivity of a polymer surface. However, the efficiency of corona treatment is limited by the development of a surface layer, composed of oxidation products of the polymer, and weakly bound to the substrate, since it can be removed by washing.